Abstract In this study, hydration stages were closely tracked in mixtures containing limestone (LS) powders to establish a correlation between microstructural parameters and performance properties. Despite the poor reactivity of LS powders, the setting duration of mixtures remained unchanged up to an LS dosage of 16%, after which a slowdown in setting time was observed. Hydrated compounds like hemicarboaluminate (Hc) were detected in pastes containing LS powders at both early and later curing periods, whereas compounds like monocarboaluminate (Mc) were only found in pastes containing LS powders at later curing periods. The Ca(OH)₂ increased with an increase in the LS dosage, showing an accelerating effect at both 3 and 28 days; however, the amount of water in hydrated compounds [found in Region 4 (a) of the thermogravimetric analysis plot] was higher only at an LS dosage of 8%. Because of the development of Hc and Mc, which increased the calcium carbo aluminate hydrates, the 8% LS addition had a beneficial influence on compressive strength during all phases of hydration. The “dilution” effect and increased porosity in the matrices, however, prevented the later-age strength from improving at higher LS dosages. It is critical to note that there was a good correlation between strength and hydrate water (HW) content since the changes in the latter were reflected in corresponding changes in the former when the LS dosage was increased from 0 to 24%. The HW content appeared to display better trends than the non-evaporable water content in correlating with the strength behaviour.
Systems of building construction. Including fireproof construction, concrete construction
Abstract Structures experience damage and deterioration over their life cycle. The recent increase in interest in sustainable development of cities is re-evaluating the long-term use of structures. Therefore, researches on the retrofitting method for existing structures is receiving high attention again. However, there are very few cases where the direct comparison between the repair and retrofitting effects of structures has been experimentally verified. In this study, retrofitting methods and repair methods with carbon fiber sheets for reinforced concrete columns under shear failure were investigated. 10 reinforced concrete columns were tested under reversed cyclic loading. As a result of the experiment, it was found that, when reinforced with CFS strips, the increase in the width of the strip serves to enhance the strength and ductility of the reinforced member by providing confinement against shear cracks occurring in concrete. It was confirmed that as the number of overlaps of CFS increased, a greater strength-enhancing effect and ductility-enhancing effect appeared. However, the two-way reinforcement of CFS did not show a great effect in improving strength and ductility. As a result of evaluating the repair performance of damaged members using CFS, it was found that the strength and ductility of the repaired specimen exceeded the original strength and ductility of the base material as well as the strength and ductility of the reinforced specimen.
Systems of building construction. Including fireproof construction, concrete construction
Abstract To minimize the seismic damage to the beam-column joint and facilitate post-earthquake repair, an innovative precast concrete (PC) beam-column joint (SCPJ) with self-centering and damage-controllable capacities was proposed. In the proposed SCPJ, the steel connector which was made up of two splice plates and an X-shaped plate, can form a rotational hinge at the joint and can be readily replaced after seismic damage. Also, unbonded post-tensioned (PT) tendons were used as self-centering elements. A design method was first developed for SCPJ to control damage within the dog-bone-shaped steel plates (DSP) and provide a comparable load-carrying capacity to a cast-in-place (CIP) joint. Afterward, numerical models for the proposed SCPJ were established using ABAQUS. The comparison between a CIP joint and a counterpart SCPJ (namely SCPJ-1) confirmed the validity of the design method. The damage was primarily localized in the DSP, while the PC components remained almost intact. Specimen SCPJ-1 showed a 30% lower residual drift ratio at the ultimate displacement than the CIP joint, demonstrating excellent self-centering capacity. Further, the systematic parametric analysis indicated that the increase of the DSP material strength and prestress level of PT tendons substantially improved the self-centering capability. The variations of the DSP thickness, the width of weakened section of DSP, and the thickness of XSP can shift the failure from DSP to XSP or PC components.
Systems of building construction. Including fireproof construction, concrete construction
Abstract In the calculation of reinforced concrete (RC) flat slabs with transverse reinforcement, punching shear resistance is one of the most critical factors. It is true that design provisions may be implemented, but they often result in significant biases and deviations from expectations. This study aims to present an optimized machine learning (ML) algorithm for estimating the punching shear resistance. Four machine learning (ML) algorithms (SVR, DT, RF, and XGBoost) with Bayesian optimization (BO) are presented in this paper to provide accurate predictions for flat slabs. The adoptability and optimization of the models are achieved through the analysis of a database of 337 test specimens with nine design parameters. Machine learning (ML) techniques are used to estimate punching shear resistance, which is compared with design provisions and equations relating to critical shear crack theory (CSCT). According to this study, Bayesian optimization is still capable of improving the performance of conventional machine learning algorithms, while the XGBoost-based model offers advanced capabilities. Predictions based on BO-XGBoost are in good agreement with actual values (MAE, RMSE, and R 2 are 0.09 MN, 0.14 MN, and 0.92, respectively) in test set. Following a detailed explanation using Shapley additive explanation (SHAP), a high-performance ML approach is used to investigate the predictive results. With the proposed optimized algorithms, it is possible to determine the punching shear resistance of flat slabs with transverse reinforcement during the preliminary stages of the construction.
Systems of building construction. Including fireproof construction, concrete construction
Masood Gholami, Fereidoon Moghadas Nejad, Amir Mohammad Ramezanianpour
Abstract Pavement engineers frequently employ concrete pavements because of their benefits such as extended lifetime, superior performance and durability, and so on. However, there are some disadvantages of these pavements such as shrinkage which may lead to cracking, warping, and limiting the length of the concrete pavement slabs. Shrinkage reducing admixture (SRA) and polypropylene fibers can be employed to prevent or control shrinkage cracking. In this study, increasing the length of concrete pavement slabs using shrinkage reducing admixture and polypropylene fiber was investigated. For mix compositions, two water–cement ratios of 0.35 and 0.4 were employed, and the percentages of SRA and polypropylene fiber utilized in mixes were 2% and 1% by weight of cement, respectively. Slump, compressive strength, third point flexural strength, electrical resistance, free and restrained shrinkage tests were carried out as the experimental programming to investigate the effect of these materials on concrete behavior and evaluate the amount of concrete pavement design parameters. Statistical analysis and RSM were used to determine the significance of each parameter and their interactions on concrete properties. It was observed that the use of SRA had no influence on workability; however, polypropylene fibers reduced the slump flow of concrete. Also, the use of SRA resulted in a decrease in mechanical properties. In addition, the use of polypropylene fibers considerably enhanced the energy absorption of concrete. Furthermore, on concrete containing SRA and polypropylene fiber, the magnitude of free and restrained shrinkage and crack width were reduced. Finally, the length and thickness of concrete pavement slabs were evaluated using the experimental results on the Tehran-Shomal freeway as a case study. The slab length could be increased by about 20% without any significant change in the slab thickness using SRA and polypropylene fiber in concrete mix composition. This can lead to an increase in construction speed, improve the durability of pavement and generally increase the quality of the concrete pavement.
Systems of building construction. Including fireproof construction, concrete construction
Abstract A new ultra-high strength concrete, in which oxidized graphene nanoplatelet (GO) and hollow glass powder (HGP) are added, has been developed by authors. This paper presents the material properties of the concrete such as workability, compressive and tensile strengths, internal micro structure (SEM and MIP) as well as air-tightness which was tested using an equipment developed in this study. Test results show that workability and tensile strength significantly increase by a small addition of HGP, and that cGO (GO product of company c) and HGP are well dispersed without agglomeration effect, resulting in more than 20% of reduction in porosity. It is also observed that air-tightness increases by 40% compared with conventional ultra-high strength concrete due to reduction in porosity; thus, new ultra-high strength concrete is anticipated to be effectively used for structures that requires air-tightness such as hyperloop tube. Consequently, it was observed that the workability and mechanical properties of UHSC were increased when cGO and HGP were used instead of silica fume (SF), and authors believe that utilization of new material would contribute to the change in manufacturing method and increase in mechanical properties of concrete.
Systems of building construction. Including fireproof construction, concrete construction
Formwork is a tool to help mold concrete with the desired size, shape, or position. In the implementation of formwork work, the selection of the type of formwork will affect the cost, implementation time, and construction quality. There are 3 (three) types of formwork in Indonesia, including conventional formwork, semi-system formwork, and system formwork. In this study, the installation and dismantling methods of conventional formwork and PERI System formwork will be analyzed, a comparison of the calculation of time and costs required for the installation and dismantling of conventional formwork with PERI system formwork in 3 different buildings, and an analysis of the economic feasibility study of PERI system formwork investment.This research is a quantitative research with the aim of knowing the comparative analysis of conventional formwork methods and PERI system formwork, then analyzing the material requirements and costs between conventional formwork and PERI system formwork and conducting an investment feasibility study analysis of the PERI System formwork. The work reviewed is on plate and beam work.The results of the study showed that the cost of procuring PERI System formwork was Rp 6,181,415,050 more expensive than conventional formwork. In the implementation of the installation and dismantling of PERI system formwork, it was faster than conventional formwork, the difference in installation production capacity was 6 m2/day, while the difference in dismantling time was 2m²/day. The investment feasibility study for the procurement of PERI System formwork is still feasible because the Net Present Value (NPV) value obtained was Rp 63,801,026, the Benefit Cost Ratio (BCR) value obtained was 1.007 and the Internal Rate Of Return (IRR) value was 9.48%.Keywords : Formwork, Conventional, PERI System, Investment Feasibility.
Abstract Supplementary cementitious materials (SCMs) such as fly ash and ground granulated blast furnace slag (GGBFS) are found to control the maximum temperature and the accompanying thermal gradients effectively. However, SCMs also lead to low early age strength development. Thus, it is crucial to understand the cracking behaviour of SCMs-based concrete affected by the mix design parameters. In this paper, the thermal cracking resistance was evaluated using a rigid cracking frame (RCF) with a computer-controlled temperature profile. The temperature profile was determined using the software ConcreteWorks by assuming the centre point of the mass concrete. The free shrinkage frame (FSF) and match-curing oven follow the same temperature profile as RCF to measure the free total deformation and time-dependent mechanical properties of concrete, respectively. An analytical model was proposed to calculate the autogenous shrinkage and the thermal stress separately. A time-dependent cracking risk coefficient allowing to estimate the risk of early age cracking of concrete was also proposed.
Systems of building construction. Including fireproof construction, concrete construction
Abstract This study evaluates and compares the performance of the commonly constructed mass housing envelops in India with alternative building envelop constructions. These alternative construction scenarios are created with a material library comprising of the available alternative roofing and walling system combinations including some common emerging construction technologies standardized and advocated by the Building Materials and Technology Promotion Council of India. The common trend of housing envelop constructions in the country involves ordinary burnt brick walls and reinforced cement concrete roofing and beam-column system which is referred to as the base case building envelop in our study. We consider initial investment costs, thermal comfort perception and the initial embodied energy in a multi-objective evaluation framework for assessing free running building envelops. Rat trap bonded brick walls, glass fibre reinforced gypsum construction, light gauge framed steel (LGFS) constructions, monolithic concrete (MC) construction system, reinforced concrete ribbed roof and compressed stabilized earth block (CSEB) walls and CSEB filler roof slabs make repeated appearances in the multi-objective optimal solution sets or Pareto optimal solution sets. CSEB construction has lowest initial embodied energy, LGFS gives minimal thermal discomfort whereas MC construction system reports least construction cost. A predominance of lean envelop constructions is observed in the Pareto optimal solution sets considering minimization of construction cost, thermal discomfort and construction embodied energy.
Aleksey A. Lopuhov, Ekaterina A. Vakhlina, Yurij N. Osipov
et al.
The article discusses the issues related to performance of competitions on the skill of usage of unmanned aircraft systems in EMERCOM of Russia. The relevance of the article is, on the one hand, due to the spread of professional skill contests in most organizations that help to improve the quality of training and creative thinking of specialists, and on the other hand, due to insufficient experience of its conduction in EMERCOM of Russia. The authors have developed and presented the recommendations on the organization of interested competitions based on the results of analysis of the publication materials concerning discussed activities in educational institutions and labor collectives of our country.
Systems of building construction. Including fireproof construction, concrete construction
Abstract The headed studs have been widely applied in steel–concrete composite structures as shear connectors. However, the tensile performance of headed studs is also key to the structural performance in many cases such as the semi-rigid composite joints including steel beam–concrete wall joint and steel column–base joint. Therefore, this study presents experimental and analytical study on the whole-process tensile behavior of headed studs. Tests on a total of 33 pullout specimens are first conducted. The tensile capacity and load–deformation behavior of the anchorage concrete, which dominates the structural performance of headed studs, are thoroughly analyzed. In addition, test data in the literature are collected for quantitatively evaluating the influence of embedment depth, bearing area, boundary conditions, and concrete strength on the tensile behavior of the anchorage concrete. On the basis of the influence evaluation, an analytical model represented by a piecewise function is proposed to describe the whole-process load–deformation behavior of the anchorage concrete and validated through the comparison between the predicted curves and all collected experimental results. Then the proposed model is applied to simulate the rotational behavior of the typical semi-rigid joint anchored by headed studs, which takes the contribution of the anchorage concrete into consideration, and is verified by experimental results. The research findings indicate that tensile behavior of anchorage concrete is crucial to the structural performance of semi-rigid joints, even for headed studs with large embedment depth and bearing area.
Systems of building construction. Including fireproof construction, concrete construction
A. Brás, Chippagiri Ravijanya, Veronica Torres de Sande
et al.
Abstract Housing units of around 20 million need to be constructed in India by 2022. One key challenge for government and industry is high demand for sustainable and affordable housing. This paper introduces the results of an industry focus group meeting with Indian Concrete Institute (ICI) and industrial associates, regarding needs for housing construction, novel products design and service life increase. Results show that present design methods for buildings and structures in India need improvement, from a whole life energy use perspective at a material and system level, service life improvement and real monitoring of buildings and structures. More than 50% of respondents are not happy with the existing buildings design codes as they do not help on energy use minimisation. Materials inefficiency in design, disconnection with real operational use and lack of durability tend to increase with high construction speed. It is highlighted that many of the technologies are not proven in local environments which is inhibiting their use, including reusing of blended ashes from agro-industry waste. Almost 240 million tonnes of CO2eq are emitted per year by Indian agricultural industry, which justify their re-use. Precast components are highlighted as a suitable solution in modular housing construction.
Abstract Concentrically braced frames (CBFs) comprise a large proportion of lateral-force-resisting systems used in steel building infrastructure around the world. Many categories of CBFs exist, including special, ordinary, and non-seismically detailed (i.e., current “R = 3” or pre-1988 construction) CBFs. Experimental testing of these different types of CBFs has shown that they have widely varying nonlinear behavior depending on the relative strengths of their yielding mechanisms and failure modes and level of ductile detailing. Numerical modeling of this range of behavior types is necessary to evaluate the seismic performance, including to quantify potential damage to special CBFs and the vulnerability of lower-ductility CBFs. Special CBFs have been the focus of many previous nonlinear modeling recommendations, including simulation of brace fracture, gusset-plate flexural strength and stiffness, and gusset-plate contribution to frame stiffness. However, recommendations for lower-ductility CBFs have not been well established. To provide important guidance for modeling these common systems, new recommendations based on the large quantity of available experimental data are proposed for simulating fracture of rectangular HSS braces with varying local slenderness, asymmetric load histories, and concrete in-fill; axial yielding of gusset plates; fracture of brace-to-gusset-plate welds; fracture of gusset-plate interface welds; post-fracture, secondary yielding mechanisms in gusset-plate interface connections; yielding beams in the chevron configuration; and buckling columns. These recommendations are validated using experiments of two-story chevron CBFs with yielding beams which simulated an existing, pre-1988 CBF (i.e., a nonductile CBF) and a subsequent repair where the braces and gusset plates were replaced.